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This application is concerned with triangulation sensors for object dimension, shape, thickness and position determination, especially at multiple locations on fast moving objects such as moving boards 28 feet long at 3 boards per second. Particularly described are, multiplexed and/or xe2x80x9cbinocular multipointxe2x80x9d sensors having multiple projected laser beams and at least two linear or matrix array cameras to view the images of the beams on the object. The invention discloses novel methods and apparatus to assure function of the device even with objects, such as lumber, having pronounced protrusions and depressions in their surface which otherwise can produce ambiguous answers unless the individual laser beams are sequentially illuminated in a time consuming manner.
Laser triangulation sensors are exemplified by U.S. Pat. No. 5,734,172 or 5,811,827 by Pryor et al., entitled Method and apparatus for electro optically determining the dimension, location and attitude of objects,. These patents discuss projection of zones of light from laser or other sources on to the part, the zones being spots, lines, grids or other patterns, and further disclose a xe2x80x9cBinocularxe2x80x9d arrangement using two detector array cameras to determine the position of images of said zones to sub pixel resolutions, each camera disposed on opposite side of the laser beam projection axis, in order to better deal with surface curvature and light reflection characteristics.
Leong et al, U.S. Pat. No. 4,937,445, entitled Apparatus for determining the distances of points on a surface from a reference axis, illustrates the use of a large number of beams, and briefly discusses problems observed in their use. Leong discloses the necessity to segment the detector array using a plurality of pre-defined zones positioned to receive respective individual returned images, which acts to allow discrimination against return images which have dropped out due to out of range conditions.
Leong et al also discloses a two camera variant in FIG. 3 of his invention, where two cameras each are set up to view a different set of projected beams on the surface. However, this is in effect a set of Siamese twinned single systems, and Leong et al do not appear to make use of this arrangement as in the binocular embodiments of the instant invention to facilitate resolution of image confusion ambiguity or other undesirable conditions caused by the surface condition of the object, which may be, for example, a moving board, or log.
It is noted that in the following discussion, the word xe2x80x9claserxe2x80x9d is meant to connote not only the laser device itself of whatever kind (typically a semi-conducting diode laser), but also any associated optics and power sources needed to assure that reliable optical energy can be delivered to a zone on the surface of the object to be measured. Typically, but not necessarily, such a zone is produced by focusing the radiation emanating from the laser to a small zone at the mean point of object location in the laser projection direction.
It is also noted that the term xe2x80x9cCCDxe2x80x9d in this application applies to all photo-detector arrays of what ever type. While the preferred detector array to date has been a CCD, or charge coupled device, type array (for example a Reticon 1 024C linear CCD type), it is anticipated that other array types can be used, such as CMOS types and that they can be sequentially scanned or randomly scannedxe2x80x94even pixel by pixel.
Laser triangulation sensors projecting multiple zones on an object which can be viewed by one photo-detector array camera operating at high speed, have found favor in industry, particularly the lumber industry where, for example, requirements exist to determine shape, thickness or local contour of 28 foot long boards moving sideways on chain conveyors at 3 boards per second, in order to control the saws used to trim the boards of non conforming stock.
Multipoint sensors, such as shown in Leong et al referenced above, have however, severe disadvantages on irregular shaped wood (increasingly the norm), in that ambiguous data can be obtained due to obscuration of projected zones in the triangulation viewing direction, typically along the object longitudinal axis. Using prior art techniques, the ambiguity problem limits accurate mensuration at high speed, increasingly an issue for modern lumber processing and manufacturing applications.
In the invention herein, two methods are disclosed to obviate the problem, which may also be used in combination if desired. First, To obviate ambiguity problems, multipoint triangulation with collimated individual lasers(or other light sources) is used in various advantageous embodiments to illuminate multiple positions on an object in a manner that allows the data to be interpreted (Alternatively, but less advantageously, a single beam can be split in to multiple beams. ). The lasers in a first embodiment herein are not all energized at once, but rather only those lasers which produce unambiguous readings are energized at any one time. By repeated sequential interrogation of the detector array using the different zone sets imaged, at the end of the process after all lasers have been energized, all zones and the resulting profiled points desired can be examined- this however, at the cost of multiple camera frames and lost time.(resulting in less spatial resolution of object shape or thickness variation for example, for any objects traveling at a given rate).
In a second set of embodiments, a more sophisticated and faster approach is disclosed which utilizes a binocular pair of photodetector array based or other TV cameras (with either line or matrix arrays)to observe the projected zones on the object (typically laser spots or short lines). Unlike Leong, each camera observes all, or substantially all of the projected zones. One or more algorithms are used to determine validity of data coming from each projected zone.
It is a goal of the invention to provide a triangulation device, employing at least one photodetector array camera and projecting on an object multiple projected laser or other light zones, which overcomes the ambiguity caused by object surface discontinuities while operating at the highest possible operational speed, with acceptable accuracy and at reasonable cost.
It is also a goal of the invention to provide such a device having multiplexed light sources which are energized on different scans of said camera or cameras, and to provide various mechanisms for optimizing the range, speed, resolution, and other attributes of such a device.
It is a further goal of the invention to provide a binocular sensor device comprised of at least two photodetector array based cameras for viewing all (or substantially all) projected zones on the object at once, and for discerning from comparison of data obtained from the cameras the range data corresponding to each zone, even in the presence of object occlusions, obscurations, or areas of unusual reflectance.
It is a still further goal of the invention to make use of unique triangulation geometry for each camera, multiplexing arrangements, array scan directions, and other sensor configurations to aid in discerning the correctness of data in the presence of object data ambiguity
It is also a goal of the invention to provide a method for measuring the location more than two projected zones on an object, using two cameras to view said zones, said cameras each viewing a field encompassing all zones projected and wherein one camera is used to confirm that the same number of zones are seen as the number seen by the other camera
It is also a goal of the invention to provide a method for measuring the location of a plurality of points on an object wherein a look up table of calibration values seen by each camera for each of the points projected on the object is provided.
It is also a goal of the invention to provide a method for measuring the location of a plurality of points on an object wherein the points are not all illuminated at once.
It is another goal of the invention to allow the reconstruction of object curved edges and other regions measured at high speed by using interpolated or extrapolated data, for example to fill in readings obtained.
It is also a goal of the invention to provide a method for increasing the reliability of detection of projected zones on objects with variant reflectance characteristics at different portions of their surface.
It is also a goal of the invention to provide a method for sorting of binocular arrangements in those cases where the binocular configuration is compromised due to physical size of placement constraints.
Finally it is a goal of the invention to provide a method for spacing projection sources such as lasers with consideration of operating window regions of the segmented output of one or more detector arrays.